In German published patent application DE-OS 2,402,586, an internal combustion engine is described wherein the energy supplied to a hot spot from an external source is adjusted to the energy requirement of the hot spot via a control arrangement. Further, British Pat. No. 1,545,865 discloses a heat ignition system for internal combustion engines wherein the electric current supplied to the glow plug is adjusted in dependence on the deviation of the actual ignition point from the desired ignition point. In both publications, therefore, the time the combustion commences is controlled by influencing the temperature of the hot spot or the glow plug. However, particularly in the operating range close to full load, this can not be sufficient any more because the heat developed in the mixture itself continues to heat up the hot spot or the glow plug, as a result of which uncontrolled ignition may occur in the engine.